Inhibiting rust formation on various metal surfaces, particularly iron-containing automotive products which are exposed to salt, is highly desirable. Various solutions for preventing rust formation have been suggested in the past. It is a well known practice to coat the under body of automobiles with materials possessing corrosion preventive properties. To this end, both in-point-of manufacture and after market applications, numerous materials and formulations have been utilized.
Most of these rust preventive corrosion compositions are based on chemically inert grease or wax-like materials. Typical of these formulations are those taught in U.S. Pat. Nos. 2,374,565, 2,430,846, 2,573,878, 2,995,532, 3,313,635, 2,746,643 and 4,150,192. In U.S. Pat. No. 3,746,643, calcium and magnesium sulfonates in a minor amount of mineral oil are taught to be useful as rust inhibitor coatings when combined with a microcrystalline wax. U.S. Pat. No. 4,150,192 teaches a sprayable hot melt rust inhibitor composite comprised of a mixture of a sulfonate, optionally a carbonate, optionally an oxidized petroleum, diluent oil, microcrystalline wax, active filler and thermoplastic resin. The composite is taught as useful for coating automobiles.
Because these prior art coating compositions are generally non-drying and lacking in cohesive strength, they can readily be removed by abrasion, impact, or elevated temperatures, and therefore require frequent inspection to determine the adequacy of the protection being afforded the coated metallic surfaces.
Elastomers have been incorporated into rust preventative compositions in an attempt to improve their cohesive strength. However, because of the extremely high viscosity of such elastomers, they can only be incorporated in a very limited quantity. The compositions containing higher levels of elastomers have a very high viscosity and cannot be sprayed unless diluted with organic solvent. However, the incorporation of such volatile solvents is undesirable for a variety of reasons, including potential fire hazard and toxicity. Epoxy resins generally have a lower viscosity than such elastomers and are known for their superior cohesive strength when used as a coating binder. However, due to the poor compatibility between epoxy resins and petroleum sulfonate complexes commonly used in rust preventative composition, epoxy resins have not been successfully blended homogeneously into such compositions.